struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};



class Solution {
public:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
        if (!root1 && !root2) {
            return nullptr;
        }
        else if (root1 && root2) {
            TreeNode* root = new TreeNode(root1->val + root2->val);
            root->left = mergeTrees(root1->left, root2->left);
            root->right = mergeTrees(root1->right, root2->right);
            return root;
        }
        else return root1 ? root1 : root2;
    }
};